New Burr Tool is Finished & Final Modifications

It's hard to believe it has already been a month since the SCAA show. We had a great time meeting the backers who stopped by the booth and the grinders performed well for the entire show.

Since SCAA we finished the new tool for the inner burr, identified some quality control issues and made a few other improvements that are all outlined below.

New Burr Tooling Finished - Good for production

The new tool for the inner burr is finished and the ceramic factory has already produced three sets of samples. The new samples of the inner burr fit properly into the outer burr and the grinder is now performing well on all grind sizes. The shrinkage rate is now properly accounted for and we are good to move forward with this tool for production.

We found some unsymmetrical variations in the dimensions on a couple of the sample burrs. For example, the diameter across the bottom is 35mm in one direction and a perpendicular measurement is 34.7mm. Since it is not a symmetrical variation, like shrinkage would cause, we think it is happening when the wet ceramic pieces are being moved to the kiln. Any small bump or shake can cause the wet ceramic pieces to deform.

Our team in Shanghai has been spending time at the ceramic factory to refine the process and the problem is only affecting a small percentage of the samples. We are setting QC guidelines to check the burrs for problems like these before they go to the assembly line.

Updated Timeline

The new burrs and other components that we made modifications to are estimated to arrive at the assembly factory by May 30th. We will then do the pilot run of 500 units during the first week of June and the full production run immediately afterwards.

This should allow us to begin shipping grinders directly to international backers from Shanghai at the beginning of July. The grinders for US backers will go onto a container ship and should arrive by the end of July with deliveries beginning in August.

Handground is coming together to be an incredible grinder and we really appreciate all of the support from the community of the decision to not compromise on quality.

Coffee Grind Sieve Analysis

In the last update we published a preliminary chart showing the particle size distribution with the first sample burrs. One of the backers reached out and informed us that there was a better way to approach particle size analysis with a sieve shaker. In fact he had already written a blog post on it: Coffee grind sieve analysis for the layman

We followed Mark's method and conducted another sieve shaker analysis. For this experiment, we tested the same three grinders, Handground, the Baratza Encore, and the Hario Skerton. We tested the three grinders for a median grind size of 850 microns (0.85mm), the medium grind size outlined in the SCAA Certified Home Brewer Guide grind analysis.

The faded blue box in the chart represents the optimal grind range, with anything falling to the left being finer ground particles and anything to the right being larger ground particles.

As you can see, Handground performed relatively in line with the Baratza Encore electric burr grinder while the Hario produced considerably more fines and slightly more large chunks of ground coffee as well. If you are not familiar with the Encore, it is a quality electric burr grinder that retails for $130. We expect the results for Handground to continue to get better with the production quality parts that have higher tolerances than the sample components.

Steps Piece Modification

After testing the new burrs we found the grind settings at the coarsest level were bigger than you would use for any brewing method. Fortunately we're able to adjust the range of coarseness easily by subtracting material from the plastic injection mold.

Previously, each step raised or lowered the inner burr by 0.2mm. By modifying the tool, we were able to raise the height of each step by 0.043 mm (0.0017 inches) so the distance between each step is now 0.157mm. The reduced distance between each step gives us more range in the middle settings for medium grinds while still giving us coarse enough grinds for any brew method in the last few settings.

This is also a good time to look at how the steps piece was designed. When the grind size adjustment ring is rotated there is a leg that travels up and down the steps in the picture above. The green face that is on the left side of the center step (pictured above) has a gentle slope and the face on the right side of the step has a steep slope. It is harder to raise the burr up, especially if there are beans in there, and easier to lower it so we designed the geometry of the steps to compensate.

Pakka Wood Knob

Old supplier on left, new supplier on right

The wood knob on the left is from the samples that we had for SCAA. There are several problems with the dimensions of the knob but the most noticeable one is the tapering angle towards the handle that creates a ledge where the knob ends and the handle begins.

We found a new supplier for the wood knobs shown on the right. The angle of the taper on the new samples matches the bottom of the handle as we originally intended. Both suppliers received the same drawings yet we do not know why one was able to accurately replicate them and the other was not.

Vertical Axle Connection

We found a problem with some of the short vertical axles that go into the gearbox in the top cap. The axle has a hexagon shaped hole drilled into the bottom with a broaching machine that allows the main vertical axle to slide up and down inside of the hole when the grind setting is changed. When this hole is drilled, some leftover metal material sometimes gets stuck in the hole. Almost 25% of the sample axles we received had metal bits stuck inside of the hole that prevented the hexagon tip on the long vertical axle from sliding into it all the way.

When you change the coarseness setting on the grinder, the hexagon tip on the long vertical axle moves up and down inside the short axle. The burrs inside the hole prevent the axle from moving up when changing to a finer grind setting.

We have already addressed this issue with the supplier and they are refining the process and setting QC guidelines to check the axles for metal burrs like these before they go to the assembly line.

Non-Slip Pad and Silicone Ring on Glass Catcher

Old pad on the left, new pad on the right

The glass catcher has a non-slip pad on the bottom that helps prevent the grinder from sliding around on the counter while it is grinding. During grind testing the non-slip pad wasn't doing it's job of preventing the grinder from slipping on the counter very well.

We started to look at why this problem was happening and found the pad was perfectly flat. The drawings we sent to the supplier had one side of the pad shaped like a dome so it would match the concave shape of the bottom of the glass catcher.

When the flat pad fit onto the concave glass it prevented the middle surface area of the pad from contacting the counter. That supplier claimed that it was not possible to make the mold with a concave shape, so we looked for a new one that could, and we found one.

The old pad also had a matte, unpolished finish on the bottom. We found that a polished surface would do a better job of sticking to the counter so we made the new tool with a polished center area that produces a shiny surface that sticks better to the counter. We could not polish the outer edge of the pad because of the small lettering around the outer circumference.

The new pad has a dome shape that matches the bottom of the glass catcher so when it's glued on the entire surface area of the pad stays in contact with the counter.

The red arrow points to the translucent white ring

One more small addition we made is a silicone ring that fits at the base of the threads on the glass catcher. There is now a snug fit as you tighten the catcher compared to when it was just glass on plastic. The ring also helps prevent the catcher from accidentally unscrewing while you are grinding.

Copper Finish

The copper sample parts are in the process of being made right now and we should have photos of them in the next update. The copper finish is done by the same factory that does the brushed nickel finish.

We can't wait to see the final samples and know that our copper backers can't wait either! The copper grinders will be shipped at the same time as all other backers' grinders from the first full production run.

Handground Content Team

We want to take the opportunity to recognize and thank everyone that has contributed as a part of the Handground Content Team. The goal is to share the collective knowledge of the coffee community and we are really proud of the progress that has been made so far.

A couple months ago we partnered with Barista Magazine to survey the specialty coffee community with the goal of learning how people discover new coffee shops, what leads to a positive experience when visiting a shop, and why customers turn into loyal fans.

Similar questions were asked to coffee shop customers and coffee shop owners/baristas to compare how perceptions differ between shops and customers.

The survey was 64 questions long and received responses from 759 customers and 392 coffee shop owners/baristas.

The data visualization shown below was made from the responses and it published in the April-May issue of Barista Magazine.